The goal of this research is to understand the neural mechanisms of associative learning in infants. Specifically, the proposed research investigates the neural substrates of postnatal olfactory learning in newborn rats. This early learning is associated with specific changes in neural structure and function in the olfactory bulb, the first central relay for olfactory information processing. Our previous work has demonstrated that output neurons in the olfactory bulb, mitral/tufted cells, modify their response patterns to odors learned during the early postnatal period. Furthermore, we have found that mitral/tufted cells receive convergent information about both odor stimuli and "reward" stimuli. Importantly, both the behavioral and neural consequences of early learning are norepinephrine (NE) dependent, as is at least one component of mitral/tufted cell response to reward. The proposed experiments examine how mitral/tufted cells are modified during olfactory associative learning and uses a combination of neurophysiological and neuropharmacological techniques to further explore the neural substrates of the descending "reward" input to the olfactory bulb. Based on preliminary data, a specific circuit is proposed for convergence of odor and reward information in the bulb involving the primary olfactory nerve and centrifugal inputs to the bulb which are known to primarily terminate on GABAergic interneurons. Each of these components will be examined in relation to early learning. The results will provide important information regarding the neural pathways and pharmacology involved in a critical form of learning expressed soon after birth in many animals including humans.